The invention relates to methods for making sulfhydryl scavenging agents having a reduced water content. Preferred are methods for making reduced water content condensation products, more preferably reduced water content bisoxazolidines.
The removal of H2S from a liquid or gaseous hydrocarbon stream is a problem that has challenged many workers in many industries. One such industry is the petroleum industry, where the H2S content of certain crudes from reservoirs in many areas of the world is too high for commercial acceptance. The same is true of many natural gas streams. Hydrogen sulfide has an offensive odor, and streams containing H2S often are called xe2x80x9csourxe2x80x9d streams. Treatments to reduce or remove H2S from hydrocarbon or other substrates often are called xe2x80x9csweeteningxe2x80x9d treatments. Even where a crude or gas stream contains only a minor amount of sulfur, the processes to which the crude oil or fractions thereof are subjected often produce one or more hydrocarbon streams that contain H2S.
The presence of H2S in hydrocarbon streams presents many environmental and safety hazards. Hydrogen sulfide is highly flammable, toxic when inhaled, and strongly irritates the eyes and other mucous membranes. In addition, sulfur-containing salts can deposit in and plug or corrode transmission pipes, valves, regulators, and the like. Flaring of natural gas that contains H2S does not solve the problem for gas streams because, unless the H2S is removed prior to flaring, the combustion products will contain unacceptable amounts of pollutants, such as sulfur dioxide (SO2)xe2x80x94a component of xe2x80x9cacid rain.xe2x80x9d
The problem of removing or reducing H2S from hydrocarbon substrates has been solved in many different ways in the past. A number of known systems treat a hydrocarbon stream with an amine, an aldehyde, an alcohol, and/or a reaction product of these agents. One such product is the product from the condensation reaction of an alkanolamine and an aldehyde.
Unfortunately, water is a natural by-product of a condensation reaction. The condensation product of an alkanolamine and an aldehyde comprises a mole of water for every xe2x80x9cNxe2x80x94Cxe2x80x94Nxe2x80x9d moiety produced. For example, bisoxazolidine produced by a condensation reaction comprises approximately 20 wt % water. It is unsafe to add a sulfhydryl scavenger comprising about 20 wt % water to a substantially water free refinery stream which is at a high temperature and under pressure.
The water content of a given sulfhydryl scavenging agent that creates a danger, and the level of the danger created, varies with the temperature and the pressure of the substrate. A danger clearly exists where a refinery stream is at a temperature of about 400xc2x0 F. or higher and a pressure of about 50 psig. If an alkanolamine/aldehyde condensation product comprising about 20 wt % water, or even less, were added to a refinery stream at such high temperature and high pressure, the water in the condensation product would rapidly vaporize and cause xe2x80x9csteam hammering.xe2x80x9d Steam hammering has been known to damage refinery equipment and has the potential to cause catastrophic rupture and release of the refinery stream into the environment. Methods of making condensation products with much lower water content are needed in order to avoid this problem.
Methods also are needed to increase the efficiency of such scavengers. For example, previously known sulfhydryl scavengers theoretically require the use of about 2-3 ppm of scavenger per ppm of hydrogen sulfide; however, the amount actually required is much higherxe2x80x94in the range of about 5-10 ppm or more per ppm of hydrogen sulfide. The inefficiency is believed to result from inadequate solubility of the scavenger in the substrate, which makes it difficult to distribute the scavenger evenly throughout the substrate.
A continuing need exists for methods of making efficient sulfhydryl scavenging agents having a water content sufficiently low to avoid steam hammering.
The present invention provides a method comprising providing a sulfhydryl scavenging agent comprising an initial water content, and treating the sulfhydryl scavenging agent to reduce the initial water content, producing a dry sulfhydryl scavenging agent having a reduced water content.